The present invention relates to a container craning apparatus and, more particularly, to a guide device for stacking containers in multiple tiers.
For craning containers, a spreader S is usually used as a suspender suspended from a container crane. The spreader S, as shown in FIGS. 27 and 28, generally consists of a spreader body 2, which is a frame of almost the same size as a container in the plan view, twist locks 3 and guides 4 located at four corners of the spreader body 2.
In lifting a container 1 by using the spreader S of such a structure, a rope 5 wound on a winch, not shown, mounted on the container crane is fed to lower the spreader S. The lowered spreader S is positioned with the guides 4 and thereafter the twist locks 3 are engaged with fittings at four corners of the container 1. Then, the rope 5 is wound up through a sheave 6 to lift the container 1 to a desired location.
In this type of container lifting or craning, containers are often stacked in two or more tiers in a keeping area. That is, a container 1 suspended by the spreader S is placed on containers already put in the keeping area. This process requires that the container being lifted should be aligned with the lower containers. To improve the efficiency of this positioning work, a container guide device with guides 4 at four corners of the spreader body 2 extending downward, for example, longer than the height of the container, has been proposed (as in Japanese patent application Kokai publication No. 50-88765).
However, the container guide apparatus of the above mentioned construction with downward-extending guides has a drawback. When the spreader S is guided to the side of the container 1, horizontal forces act on the guides and tend to move them laterally, producing large bending moments in the bases of the support members for the guides.
The container can be as high as 2.9 meters; and because the spreader must be supported by support members that long, the support members are subjected to large bending moments. To withstand such bending moments requires the support members to have a great mechanical strength and therefore a larger structure.
However, since containers are placed in multiple rows with narrow intervals, it is impossible to obtain a large depth of the cross-section of the support members, so that containers should be constructed of heavy steel plates, increasing the weight of containers. Therefore, the overall weight and the cost of the crane are increased significantly. This proposed guide device is impractical.